The present invention relates to magnetic circuit breaker construction including a moveable magnetic core contained within a transparent tube. More specifically, the present invention relates to the use of a transparent tube which may be filled with liquids of varying viscosity, a core and spring, the assembly of which can be observed through the tube side walls, in order to control the rate of movement of the core toward a pole piece in response to overload currents tending to actuate the breaker contacts opened.
In the prior art the applicant's assignee has developed a variety of techniques for controlling the rate of movement of a moveable magnetic core toward a pole piece so as to actuate an armature to open breaker contact. One of the techniques employed is to employ liquids of different viscosity within the tube to control the rate of movement of the core and thus to vary the delay before the contacts open in response to an overload current. In the presence of ordinary levels of current the core will not be actuated. Frequently this is accomplished by a spring which opposes movement of the core until the force of the spring is effectively overcome. At that point how fast the contacts are opened depends upon how fast the magnetic core moves to the pole piece to attract the circuit breaker mechanism to open the contacts, which in turn depends upon the viscosity and the level of fluid in the tube. Because the tubes in the past have been opaque, it has been difficult to control the level of the filling of the tubes which is one of the parameters effecting the rate of movement of the core. The applicant has made the tube transparent so that the level of fluid and the quality of the assembly can be visually observed.